Conically mating explosionproof housing and cover assembly

ABSTRACT

The threads by which a cover is secured to a housing for electrical elements are positioned on mating conical surfaces. The taper of the threaded conical surfaces is sufficient to permit bringing the threads on the cover down over most of the threads on the housing by simply axially mating the cover with the housing. A few turns of the thus positioned cover brings all the threads into engagement to provide an &#39;&#39;&#39;&#39;explosionproof&#39;&#39;&#39;&#39; closure, e.g., with six full threads engaged. Stop-lock means prevent advance of the cover to zero clearance between threads and prevent inadvertent partial unthreading.

United States Patent Arthur 1. Appleton Bridlewood Road, Northhrook,111. 60062 [2l] Appl. No. 017,499

[22] Filed Mar. 9,1970

[45] Patented June 1,1971

[72] Inventor [54] CONICALLY MATlNG EXPLOSIONPROOF HOUSING AND COVERASSEMBLY 8 Claims, 6 Drawing Figs.

[52] US. Cl 174/52, 174/50, 220/39, 317/120 [51] Int. Cl l-l05k 5/00[50] Field of Search 174/50, 52;

220/394, 39 A, 39 8,39 C, 55 D, 55 K; 285/91, 84, 83,333,334;3l7/l20,99

[ 56] References Cited UNITED STATES PATENTS 1,776,280 9/1930 Boyd285/9lX 3,037,154 5/1962 Arneberg 3,393,824 7/1968 Appleton PrimaryExaminer- Darrell L. Clay AttorneyDarbo, Robertson & VandenburghABSTRACT: The threads by which a cover is secured to a housing forelectrical elements are positioned on mating conical surfaces. The taperof the threaded conical surfaces is sufficient to permit bringing thethreads on the cover down over most of the threads on the housing bysimply axially mating the cover with the housing. A few turns of thethus positioned cover brings all the threads into engagement to providean explosionproof" closure, e.g., with six full threads engaged.Stop-lock means prevent advance of the cover to zero clearance betweenthreads and prevent inadvertent partial unthreading.

itlllllllllllllll PATENTEU JUN 1 |97l SHEET 1 [IF 2 llllllllll Hm] Illlllll PATENTED JUN 11911 3; 582.535

sum 2 or 2 CONICALLY MATING EXPLOSIONPROOF HOUSING AND COVER ASSEMBLYBACKGROUND OF THE INVENTION To be approved for use in hazardous areas,and to meet the standards set for so-called explosionproof" equipment bywell recognizedand authoritative agencies (e.g., UnderwritersLaboratories), housing and cover assemblies must be joined by aspecified number of full threads. The number of threads specifieddepends on the particular classification of the hazardous atmosphere inwhich the assembly is intended to be used, and upon the closeness of fitof the threads themselves. The number of threads is not specified on thebasis that that number of threads is required to hold the cover in placeduring an explosion. The number of threads is required to provide asufficient path tov arrest flame propagation therebetween in the eventof an internal ignition.

Inasmuch as relatively close fit exists between mating threads ofequipment heretofore available, grit, dirt, and other foreign materialstend to either damage the threads, or make threading of the cover ontothe housing relatively difficult. It has been observed that service men,rather than struggle with a hard-to-tum cover to bring the entire set ofthreads into engagement, tend to merely start the cover onto the housingand may turn the cover only a sufficient number of turns, e.g., two orthree turns, to hold the cover to the housing.

Another difficulty encountered in handling relatively large coversheretofore available, e.g., fifteen inches in diameter, results from thefact that these elements are relatively cumbersome, bulky, and difficultto precisely manipulate. It has been found that considerable difficultyis encountered in properly starting the threading of relatively largecovers. There is a decided tendency 'to damage a number of the threadsbecause of a bad start", i.e., because of cross threading.

The tendency of the heretofore conventional housing and cover assembliesto cross thread, with resulting damage of threads is believed to be avery serious one. Replacement of a housing is no simple matter, andusually involves interruption of service, and replacement or transfer ofelectrical contents. It sometimes involves the services of severaltrades classifications, e.g., electricians, millwrights, etc. Thetendency to leave a damaged housing and cover assembly in service longerthan it should be is very strong, according to my observations.

Another problem encountered in connection with heretofore conventionalhousing and cover assemblies has been galling and otherfriction-generated damage to threads, as well as the freezing" orintegration of zero clearance abutting opposing thread faces,particularly in aluminum equipment. The problem is mainly associatedwith jamming of threads upon complete engagement therebetween. In orderto alleviate this problem and in order to facilitate the threading ofone member on the other it has been common practice to apply oil orgrease to the threads. However, the presence of oil or grease furtherexaggerates the tendency of the threaded surfaces to become contaminatedwith dust or grit and the un' desirable consequences of this werediscussed hereinbefore. A stop mechanism, disclosed by me in my US. Pat.No. 3,393,824 virtually eliminated the jamming problem.

It is an object of this invention to provide a housing and coverassembly for electrical devices, which assembly pro vides the fullnumber of meshed threads required in order that the resulting electricalarticle meet explosionproof standards, and yet which does not requiremaking a large number of threading turns. lt is another object of thisinvention to provide a housing and cover assembly in which the cover isstarted" without a tendency to cross thread" and in which it isvirtually impossible to damage the threads due to a bad start, orjam thethreads due to overengagement.

It is a further object of this invention to provide a cover housingassembly which affords explosionproof protection for an electricalarticle, which assembly does not require the use of grease or oiltofacilitate smooth and rapid turning of the members with respect to oneanother. It is a further object to provide a cover-housing assemblywhich is not significantly subject to freezing."

SUMMARY OF THE INVENTION In accordance with this invention the matingsurfaces of a cover and housing for an electrical article are generallyconical, and mating threads sufficient in number to qualify theresulting enclosure as explosion proof, are engageable on the matingconical surfaces. The taper of the threaded conical surfaces issufficient to permit most of the threads to overlap by simply axiallymating the cover with the housing. An antirotation lock is essential toprevent undesirable increase in clearance between threads caused byrelatively small unthreading rotation.

DESIGNATION OF THE FlGURES FIG. 1 is a perspective view of an invertedelectrical housing-cover assembly improved in accordance with thisinvention.

FIG. 2 is a partially cross-sectional elevational view takenapproximately along the line 33 of HG. 1, except that the cover isrotated approximately and is being lowered onto the housing member.

FIG. 3 is a fragmentary cross-sectional view taken approximately alongthe line 33 of FIG. 1.

FlGS. 4, 5, and 6 are plan views of the housing, showing alternativeembodiments for use with single-, double-, and tripie-lead threadsrespectively.

DESCRIPTION OF PREFERRED EMBODIMENTS Although the following disclosureoffered for public dissemination, in return for the grant of a patent,is detailed to ensure adequacy and aid understanding, this is notintended to prejudice that purpose of a patent which is to cover eachnew inventive concept therein no matter how others may later disguise itby variations in form or additions or further improvements. The claimsat the end hereof are intended as the chief aid toward this purpose, asit is these that meet the requirement of pointing out the parts,improvements, or combinations in which the inventive concepts are found.

The objects set forth above, and other objects which are apparenthereinafter are all accomplished by the housing and cover assembly ofthis invention. In the embodiment illustrated (which has been invertedin the drawings for illustration purposes) in FIGS. l-4 of the attacheddrawings, domeshaped cover or cap 10 connects with housing 12 by meansof mating threads l5, 16, may be considered as cut from the inside andoutside, respectively, of conical surfaces, and the taper of therespective conical surfaces in the illustrated embodiment is sufficientto permit approximately four complete threads to overlap one another asa result of merely positioning cover 10 with axial movement only overthreads 16 (see FlG. 2). Subsequently, after two complete turns of cover10 to thread it onto housing 12, the resulting connection includes themeshing of six threads (see FIG. 3).

HOUSlNG Housing 12 includes enlarged middle enclosure section 18 withinlet and outlet connectors 20, 22, respectively, which provide alignedpass-through channel 23 close to one side 24 of housing 12. Thispass-through channel 23 facilitates pulling wire through the enclosurewithout the necessity of removing the contents of housing 12 or cover10. Details of the means by which connectors 20, 22 are fastened toconduit, pipe, or to another electrical enclosure in a bank, are notshown since they are conventional and do not constitute part of theinventive concept. Enclosed end portion 26 may be an integral part ofhousing 12, i.e., integral with enlarged portion 18, but alternativelymay be provided in the form of a second removable cover substantiallyidentical to dome-shaped cover 10. In such an embodiment, the means ofconnection, in accordance with this invention, would be identical to thethreaded connection illustrated in the FIGS. 2 and 3 of the attacheddrawings.

Housing 18 includes mounting bracket 30 in internally fixed thereto in aconventional manner, and bracket 30 includes threaded openings 32 orother means for attaching electrical components thereto. Examples of thekinds of electrical components which are housed in housing and coverassemblies in accordance with this invention include circuit breakers,line starters, and other electrical articles, none of which areillustrated because they are conventional. The invention is notdependent upon the particular electrical components housed in theenclosure.

it is not necessary that cover be dome shaped as in the illustratedembodiment although the presence of the relatively large enclosed region36 permits mounting of electrical articles on bracket 30, which articlescan extend through opening 38 of housing 12 into region 36 withindome-shaped cover 10. Thus, in such a utilization of the housing andcover assembly of this, invention in accordance with the illustratedembodiment, removal of cover 10 exposes a large bulk of an enclosedelectrical article tofacilitate the servicing thereof. Alternatively,mounting brackets 30 equipped with conventional swingout or pivot outmounting features can be used to facilitate servicing of componentsnormally residing within enlarged portion 18, upon removal of cover 10.

Mouth 38 of housing 12 passes through generally conical neck 40. Threads16 are positioned on the exterior portion of neck 40. Radially extendingflat portion 42 joins the base of neck portion 40 with sidewalls 44. Inthe illustrated embodiment sidewall 44 is extended axially to providelip 46. Lip 46 is employed as a drip lip (when the embodiment is turnedright side up) so that water will not run from the sides, across thebottom and into the threads. Its presence also assists in protectingthreads 16 from mechanical damage while cover 10 is removed.

Radial portion 42 includes detent socket 50, the function of which willbe described in further detail hereinafter.

COVER Cover 10 is generally domelike, and includes closed end 52,substantially cylindrical sidewall 54, and outwardly tapering sidewallportion 56. In the illustrated embodiment the end of tapered sidewallportion 56 continues radially as extending flat faced flange 58. Anenclosure 60 for the releasable lock mechanism, generally 62, is mountedon the side of cover 10. As illustrated, it has been cast as an integralpart of the outwardly tapering portion 56 but could be a separable partaffixed to the cover. Releasable detent mechanism 62 includes slideablebolt 64, collar 66 fixed thereto, compressed biasing spring 68, andexternally accessible release knob 70 which is secured to bolt 64 bymeans of setscrew 72. Spring 68 is retained within enclosure 60 bycollar 66, and, though bolt 64 is retractable into enclosure 60, knob 70limits its motion in the extending direction. Adjustment of the lengthof extension by changing the point at which bolt 64 is engaged bysetscrew 72 may be necessary for reasons explained more fullyhereinafter.

A critical relationship exists between the positioning of threads 15,16, the positioning of detent mechanism 62, the positioning of detentsocket 50 on radial surface 42, and the reach of bolt 64. The relativepositioning of the threads l5, l6, releasable lock mechanism 62 anddetent 50 must be such that external reaching portion 74 of bolt 64 doesnot prematurely engage face 42, i.e., detent socket 50 before cover 10is turned its final turn. Moreover, it is also essential in accordancewith this invention that end 74 of bolt 64 falls into detent 50 whilecover 10 is being threaded onto housing 12 before threads 15, 16 reach azero clearance condition therebetween. This not only preventsunnecessary abuse of threads 15, 16, but, as a result of preventing zeroclearance abutment of surfaces (e.g., complete mating) of threads 15,16, galling and long term integration of the surfaces, particularly inthe case of aluminum threaded components, is virtually eliminated. Theengagement of bolt 64 with detent 50 must occur after a sufficientnumber of threads 15, 16 have engaged to qualify the element asexplosionproof" for the particular use intended, and just before a zeroclearance condition is reached, e.g., within oneeighth of a turn,preferably about 5 to 10 rotation from zero clearance condition.

HOUSING-COVER RELATIONSHIP The following manufacturing procedure issuggested primarily to illustrate the critical relationship which wasreferred to above. Prior to the final adjustment of the reach of bolt64, and prior to the placement of detent socket 50 in radial face 42,cover 10 is threaded gently into complete engagement with housing 12.When further rotation of cover 10 with respect to housing 12 isimpossible, due to the complete engagement of threads 15, 16, cover 10is rotated in the reverse, or unthreading" direction through a verysmall are sufficient to provide the desired clearance between opposingthreads. I presently prefer between 0.005-inches and 0.0lO-inchesclearance at the sides of the threads and about 0.005- inches differencein pitch diameter. However, the amount of clearance can be set at anydesirable or necessary value, by proper placement of lock socket 50. Thedesired clearance (e.g., difference in pitch diameter) may be used incalculations based on rate of advance of opposing core surfaces perturn, to determine the precise are through which the cover must beunthreaded to achieve that clearance. For example, with a single leadthreaded system on 30 included angle cones i prefer a backup arc of 5 to10 from zero clearance. Generally I prefer that the difference betweenthe lock-stop position and the zero clearance position be less thanone-sixteenth ofa revolution after the cover is unthreaded through thepredetermined arc, the point at which end 74 of bolt 64 then touchesradial portion 42 is then marked. Cover 10 is then completely unthreadedfrom housing 12 and detent socket 50 is cut into radial portion 42 atthe point marked. Cover 10 is then rethreaded onto housing 12,retracting bolt 64 manually by elevating release knob 72, if necessary.Threading is continued to the point of complete engagement of threads15, 16 by gently advancing or rotating cover 10 onto the threads ofhousing 12 until further rotation is again impossible. Release of knob72, and reversing rotation of cover 10 slightly brings bolt 64 intoalignment with detent socket 50. At this point spring 68 urges end 74 ofthe bolt 64 into engagement with socket 50. The housing and coverassembly is now in operating position.

To complete the final adjustment of the assembly in accordance with thisinvention, release knob 72 is manually elevated until end 74 of bolt 64clears detent socket 50. Cover 52 is then rotated in the unthreadingdirection until end 74 is at a point approximately three-quarters of aturn away from socket 50, i.e., within about one-quarter of a turn ofbeing realigned, for the first time during unthreading rotation, withsocket 50. At this point setscrew 72 is loosened and release knob 70 isadjusted on bolt 64 so that knob 72 rests, at this point, on top ofenclosure 60. Upon retightening setscrew 72, the end 74 of bolt 64 isthus adjusted so that it does not engage socket 50 except at thecompletion of the last threading turn.

it is not essential that end 74 of bolt 64 engage housing 12 almost acomplete turn prior to engagement with socket 50. It is, however,important that end 74 of bolt 64 cannot engage detent 50 prematurely,i.ei, until immediately before the jamming point is reached. Prematureengagement of bolt 64 with socket 50, e.g., during the second to lastthreading turn, would leave an excessively great clearance, or anexcessively loose fit" between the threads. End 74 of bolt 64 may beadjusted to engage housing 12 at any point during the last revolution,although if too small an arc is turned between the initial engagement ofbolt 64 with face 42 and the point at which it seats in socket 50, thedepth to which end 74 reaches into socket 50 may beinadequate to providea reliable lock of the cover against rotation with respect to housing12. Generally speaking, therefore, the reach of bolt 64 beyond the faceof the member in which it is mounted cannot equal or exceed the axialdistance between adjacent threads 15, or 16.

It is desirable that latch or detent 62 not be on the back of the unitwhen it is mounted. To achieve this, one procedure would be to make thedetent enclosure a separable part and not to affix it on the cover 10,until after the threads were formed. At that time the cover would bethreaded onto a standard housing 12 and the proper position for theenclosure 60 marked on cover 10 so that the enclosure could be put inplace in the proper position.

In the embodiment of FIGS. l4, a single lead thread is utilized andconsequently only a single stop point or jam point is possible uponcomplete engagement of the threads. If a double lead thread wereutilized it is apparent that two jam" points would be possible. In suchan embodiment (FIG. 5) two detents 80 are placed in accordance with theabove described procedure, and the end of bolt 64 is adjusted toinitially contact face 42 within the last half turn of the threadingrotation. In the event a triple lead thread is utilized (FIG. 6) threejam" points are possible. Consequently three detents 81 are placed onface 42 in accordance with the above described procedure. Again, inaccordance with the above described procedure the end of bolt 64 isadjusted in the latter mentioned embodiment to engage the face 42 in thefinal third of a turn. Obviously, the stop means utilized in conjunctionw9th double, triple, and other multiple thread embodiments could includeuse of multiple lock mechanisms 62 in conjunction with a single socket50. However this alternative construction would necessitate the use of alarge number of structural parts, and would be considerably moredifficult to precisely adjust.

It must be emphasized that releasable lock mechanism 62 is essential inaccordance with this invention. Because of the relatively large changein clearance between threads which occurs during a relatively small arcof threading or unthreading rotation, and because the magnitude of theclearance between the threads greatly affects the efficacy of theresulting threaded connection for the purpose of arresting propagationof a flame front therebetween, it is essential that the housing and thecover assembly be provided with positive locking mechanism to preventeven a small quantum of rotation in the unthreading direction.Therefore, providing mere stop means which prevents advance of the coverto the point at which the engaging threads would jam is inadequate andnot at all acceptable, due to the fact that the clearance between thethreads depends greatly on the extent to which the threads are engagedin this invention.

GENERAL DISCUSSION The taper of neck 14, and consequently of threads 16mounted thereon, and the conical taper of tapered portion 56, and ofthreads 15 on the inner face thereof, must be sufficiently great topermit most of threads 15, 16 to overlap as a result of axial movementof threads 15 over threads 16, except for that number of threads whichwill be engaged by three or less turns of threads 15, 16 with respect toeach other.

The Underwriter Laboratories standard for explosionproof equipment ingroup C and D environment (which includes ethyl-ether, acetone, andgasoline mixtures with air) is five full threads. One large manufacturerof explosionproof" electrical fixtures uses at least six threads toprovide an even greater margin of safety. Thus in an embodiment of thisinvention in which six threads is specified for fully engaged condition,the taper of neck 40 and tapered walls 56 must be sufficiently great topermit the overlap of at least three threads and preferably fourthreads, as a consequence of the axial mating of cover 10 onto housing12.

The Underwriter Laboratories standard requires a larger number ofthreads for other environments, for example for groups A and B whichinclude the acetylene-air and the hydrogen-air mixtures. Those skilledin the art, given the subject matter disclosed herein can readilyutilize the subject matter disclosed herein in the manufacture ofexplosionproof fixtures having any number of threads required forparticular environments for which the fixtures are to be used.

In the embodiment illustrated in FIGS. 1 through 4 threads 15, 16 aresingle-lead threads. The upper end or beginning 76 of thread 16 isperhaps best seen in FIG. 4. However, as sug gested hereinbefore, it isnot essential that a single thread, or single-lead thread be used inaccordance with this invention. It is considered within the purview ofthis invention that multiple lead threads, for example double or triplethreads, may be util ized. Thus, in FIG. 5, two beginnings 77 of adouble-lead thread are indicated. In FIG. 6 the three beginnings 78 ofatriple-lead thread are indicated. In the event a double-lead thread isutilized, as suggested in FIG. 5, it is necessary that double-detentsockets 80 be utilized; in the event a triple lead thread is used, threedetent sockets 81 are utilized, and so on.

The use of single lead threads has the advantages that these threads areeasier to machine, there is only one stop point, and, due to therelatively slow advance per revolution, rotation of the cover through asmall arc causes a relatively small change in clearance between opposingsurfaces of threads 15, I6. Multiple-lead threads have the advantage ofproviding relatively great axial advance per given rotation of cover 10.However, if a double-lead thread is used bolt 74 must be sized andadjusted to contact face 58 at a point between sockets 80 in the last orfinal part of rotation of cover 10 prior to its engagement in thatsocket 80 which stops rotation just prior to zero clearance condition,i.e., within one-half turn of the final socket 80. Likewise when atriple thread is utilized it is necessary to provide three sockets 81 ata position such that rotationalmotion of cover 10 is locked immediatelybefore thezero clearance condition is reached, and bolt 74 must be sizedand adjusted to engage face 58 between sockets 81 in the last or finalportion of the rotation of cover l0just prior to engagement by bolt 74with that socket 81 which stops rotation just prior to zero clearance,i.e., within onethird turn of final socket 81.

As a result of my observation of the use and abuse of explo sionproofhousing and cover assemblies over a period of years I have concludedthat the improvement of this invention must not require more than threeturns in order to bring the specified standard number of threads intoproper mating engagement. It is highly preferred that only two or lessturns be required.

In the illustrated embodiment in which a single-lead thread isillustrated, the taper of neck 40 and sidewalls 56, i.e., the taper ofthe cone in which threads 15, 16 may be considered to be located, isapproximately 30 at the tip or point of the cone, i.e., at the includedangle. In this embodiment, in which six threads are fully engaged whenbolt 74 engages socket 50, four threads overlap as a result of the axialmovement of the cover 10 over neck 40, and two additional turns arerequired to completely, i.e., properly, mesh six full threads.

Although full square threads or Acme threads are imminently satisfactoryfor use in accordance with this invention, provided adequate clearanceis provided at the sides of the full square" threads, I prefer to use amodified square thread, that is, a thread having between 7.5 and 10taper on the tooth.

Removal of cover 10 from housing 12 in accordance with the use of thisinvention, is an extremely simple matter. Release knob 72 is withdrawnsufficiently to permit bolt 64 to clear socket 50, and cover 10 isturned in the withdrawal direction. Only two turns are required to movecover 10 axially a sufficient distance for threads 15, 16 to disengageand to permit cover 10 to be withdrawn axially without further turningaction. As soon as turning starts, the clearance between threads, i.e.,the difference in pitch diameter, increases rapidly as one conewithdraws from the other. Hence, turning becomes less hindered due tofriction as unthreading continues.

ln accordance with this invention, socket 50 can be positioned toterminate pivoting of cover 10 when threads l5, 16 are very close tozero tolerance, i.e., in a condition of very close fit. As indicatedabove the number of threads which must be fully engaged to qualify ahousing-cover assembly as explosionproof in accordance with UnderwriterLaboratories standards, depends not only on the nature of the intendedenvironment, but also on the closeness of the fit of the threadsthemselves. it will be appreciated that the closer the fit of thethreads during operation, the greater the effectiveness of the threadedconnection with respect to arresting the propagation of an ignitionfront therebetween. Thus the combination ofengaging threads on taperedmating faces, and stop means in an explosionproof cover-housing assemblyof this invention is particularly advantageous.

l have been unable to cross thread cover 10 onto neck 40, and l haveasked others to attempt to do so. To my knowledge all attempts to do sohave failed. When cover 10 is moved axially over neck 40 to the limit ofaxial mating engagement therewith, the alignment of cover 10 withrespect to housing 40 is virtually perfect, and slight deviation fromperfect alignment seems to be automatically corrected when cover It) isturned over neck 40 to begin threading of threads l5, 16 without crossthreading. Hence, this housing and cover assembly virtually eliminatesthe risk of thread damage due to cross threading, the nuisance of havingto replace or rehouse electrical components in hazardous areas becauseof cross threading damage to threads, and hence also eliminates the riskof leaving a closure, damaged as a result of cross threading, inservice.

lclaim:

l. in an explosionproof electrical enclosure comprising a threaded cap,and a housing having opening means including a threaded collar matedwith said cap, said collar being positioned around said opening, theimprovement in which:

said collar and cap are threaded at tapered mating portions thereof,said tapered mating portions being inclined to such an extent that thecap is initially seatable over the collar at a point at which all butthree or less of the matable threads in said collar and cap are inopposition to each other; and

in which said enclosure includes locking means locking the cap withrespect to rotation between said collar and said cap, said locking meansbeing automatically, releasably actuatable to lock the cap at a stoppoint at which the cap is threaded to engage a sufficient number ofthreads for the resulting connection to be classified as explosionproof,said stop point being spaced apart from the point of rotation at whichopposed mating threads would actually meet at zero clearance.

2. The improvement of claim 1 in which the threaded portions areprovided with six complete turns of a single lead thread, and whereinthe tapered portions are so inclined that the cap is axially seatableover at least four turns of the thread without turning said cap.

3. The improvement of claim 1 in which the threaded portion of both thecap and collar are provided with three complete turns of a doublethread, wherein the tapered portion is inclined to such an extent thatthe cap is initially axially seatable over the collar to a point atwhich all but one or less of the complete turns of the matable threadsare in opposition to each other without threading of the cap onto thecollar, there being twojam-points at which fully engaged threads are nolonger rotatable, and in which the locking means includes means stoppingrotation just ahead of both jam points.

4. An improved quick-release nonjamming housing and cover assembly forelectrical components comprising the combination:

a housing having a neck portion and an opening passing through said neckportion, said neck portion of said housing having the configuration of atruncated cone, the

outer surface of said neck portion being tapered outwardly with respectto the housing and inwardly with respect to said opening, said neckportion having external threads extending away from its outer surface;

a cover over said opening having an internally threaded rim in threadedengagement with the threads on the conical surface of said neck portion;and

lock means preventing rotation of said cover and said housing withrespect to each other, said lock means including releasable bias meansautomatically stopping the threading rotation of the cover with respectto the housing within the last eighth ofa turn immediately precedingthat point of rotation at which a condition of zero clearance wouldexist with respect to opposed threads on said housing and cover.

5. The assembly of claim 4 in which the threads provide six completeturns of a single lead thread, and wherein the tapered portions are soinclined that the cap is axially seatable over at least four of thethreads without turning said cover.

6. The assembly of claim 4 in which the threaded portion of both thecover and housing have three complete turns of a double lead thread,wherein the tapered portions are inclined to such an extent that thecover is initially axially seatable over the tapered portion of thehousing to a point at which all but one or less of the complete turns ofthe matable threads are in opposition to each other without threading ofthe cover onto the tapered portion of the housing;

the resulting structure being capable of two relative positions of saidcover with respect to said housing referred to herein as zero clearancepoints, at which zero clearance would be obtained between opposingthreads; and

in which the lock means include means automatically stopping rotation ofthe cover with respect to the housing at a point immediately ahead ofthe zero clearance points.

7. A housing and cover assembly for use with electrical componentsincluding:

an annular housing portion;

means for mounting electrical components in said housing portion;

line access means for providing ingress and egress from said housingportion, said line access means intersecting the housing portion;

said housing portion having equipment access opening means havingsubstantially circular sidewalls tapering outwardly with respect to saidhousing portion and tapering inwardly with respect to said opening, saidsidewalls having threads extending away from said sidewalls on theexternal face thereof;

a cover portion over said opening having a substantially circular mouthand being of hollow, domelike configuration enclosing a substantialregion in which electrical components can reside, the walls of the mouthhaving threads on the inner face thereof, said mouth and said threadsbeing mated with the threads on said sidewalls of said housing;

one of said portions including releasable lock means extending axiallybetween opposing parts of said cover portion and housing portion, saidlock means comprising a slideable bolt, bias means urging the extensionof said bolt axially, release means for manually retracting the bolt;

socket means on the other of said portions engaging said bolt, saidsocket means being positioned to engage said bolt to lock the coverportion against rotation with respect to said housing portion at apointjust ahead of the point at which zero clearance would be obtainedbetween the threads on the housing and cover portions;

said bolt being of sufficient length to initially engage the otherportion on the last revolution prior to locking at a point ahead of saidsocket means.

8. A housing and cover assembly for use with electrical componentsincluding:

a housing member;

means for mounting electrical components in said housing member;

line access means for providing line ingress and egress from a coverover said opening, said cover having a substantially circular mouthhaving an inner wall having the configuration of a truncated cone, thewall of the mouth having threads on the inner face thereof, said mouthand said threads being mated with the threads on said sidewalls of saidhousing;

said cover including releasable lock means extending axially betweenopposing portions of said cover and housing member, said lock meanscomprising a slideable bolt, bias means for urging the extension of saidbolt axially, release means for manually retracting the bolt;

socket means on said housing engaging said bolt, said socket means beingpositioned to engage said bolt to lock the cover against rotation withrespect to said housing at a point within about 10 rotation ahead ofthat point of rotation at which zero clearance would be obtained betweenthe threads on the housing member and the cover;

said bolt having a reach less than the axial distance between adjacentthreads on said sidewalls.

STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. a 582,535Dated June lnventofls) Arthur I. Appleton It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 1, line 49, "The" should read -'I'his--. Column 2, Line 49, after"16," insert on mating cover 10 and housing 12 respectively. Threads l5,l6,. Column 3, line 3, should be deleted. Column 4, line 31, "threaded"should read --thread. Column 5, line 30, "w9th" should read with--.

ll ll Signed and sealed this lhth day of December 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer ActingCommissioner of Patents FORM PO-1OSO (10-69) USCOMM-DC 60376-969 w us,sovznummv PRINTING OFFICE: was o-au-su

1. In an explosionproof electrical enclosure comprising a threaded cap,and a housing having opening meAns including a threaded collar matedwith said cap, said collar being positioned around said opening, theimprovement in which: said collar and cap are threaded at tapered matingportions thereof, said tapered mating portions being inclined to such anextent that the cap is initially seatable over the collar at a point atwhich all but three or less of the matable threads in said collar andcap are in opposition to each other; and in which said enclosureincludes locking means locking the cap with respect to rotation betweensaid collar and said cap, said locking means being automatically,releasably actuatable to lock the cap at a stop point at which the capis threaded to engage a sufficient number of threads for the resultingconnection to be classified as explosionproof, said stop point beingspaced apart from the point of rotation at which opposed mating threadswould actually meet at zero clearance.
 2. The improvement of claim 1 inwhich the threaded portions are provided with six complete turns of asingle lead thread, and wherein the tapered portions are so inclinedthat the cap is axially seatable over at least four turns of the threadwithout turning said cap.
 3. The improvement of claim 1 in which thethreaded portion of both the cap and collar are provided with threecomplete turns of a double thread, wherein the tapered portion isinclined to such an extent that the cap is initially axially seatableover the collar to a point at which all but one or less of the completeturns of the matable threads are in opposition to each other withoutthreading of the cap onto the collar, there being two jam points atwhich fully engaged threads are no longer rotatable, and in which thelocking means includes means stopping rotation just ahead of both jampoints.
 4. An improved quick-release nonjamming housing and coverassembly for electrical components comprising the combination: a housinghaving a neck portion and an opening passing through said neck portion,said neck portion of said housing having the configuration of atruncated cone, the outer surface of said neck portion being taperedoutwardly with respect to the housing and inwardly with respect to saidopening, said neck portion having external threads extending away fromits outer surface; a cover over said opening having an internallythreaded rim in threaded engagement with the threads on the conicalsurface of said neck portion; and lock means preventing rotation of saidcover and said housing with respect to each other, said lock meansincluding releasable bias means automatically stopping the threadingrotation of the cover with respect to the housing within the last eighthof a turn immediately preceding that point of rotation at which acondition of zero clearance would exist with respect to opposed threadson said housing and cover.
 5. The assembly of claim 4 in which thethreads provide six complete turns of a single lead thread, and whereinthe tapered portions are so inclined that the cap is axially seatableover at least four of the threads without turning said cover.
 6. Theassembly of claim 4 in which the threaded portion of both the cover andhousing have three complete turns of a double lead thread, wherein thetapered portions are inclined to such an extent that the cover isinitially axially seatable over the tapered portion of the housing to apoint at which all but one or less of the complete turns of the matablethreads are in opposition to each other without threading of the coveronto the tapered portion of the housing; the resulting structure beingcapable of two relative positions of said cover with respect to saidhousing referred to herein as zero clearance points, at which zeroclearance would be obtained between opposing threads; and in which thelock means include means automatically stopping rotation of the coverwith respect to the housing at a point immediately ahead of the zeroclearance points.
 7. A housing and cover assembly for use withelectrical components including: an annular housing portion; means formounting electrical components in said housing portion; line accessmeans for providing ingress and egress from said housing portion, saidline access means intersecting the housing portion; said housing portionhaving equipment access opening means having substantially circularsidewalls tapering outwardly with respect to said housing portion andtapering inwardly with respect to said opening, said sidewalls havingthreads extending away from said sidewalls on the external face thereof;a cover portion over said opening having a substantially circular mouthand being of hollow, domelike configuration enclosing a substantialregion in which electrical components can reside, the walls of the mouthhaving threads on the inner face thereof, said mouth and said threadsbeing mated with the threads on said sidewalls of said housing; one ofsaid portions including releasable lock means extending axially betweenopposing parts of said cover portion and housing portion, said lockmeans comprising a slideable bolt, bias means urging the extension ofsaid bolt axially, release means for manually retracting the bolt;socket means on the other of said portions engaging said bolt, saidsocket means being positioned to engage said bolt to lock the coverportion against rotation with respect to said housing portion at a pointjust ahead of the point at which zero clearance would be obtainedbetween the threads on the housing and cover portions; said bolt beingof sufficient length to initially engage the other portion on the lastrevolution prior to locking at a point ahead of said socket means.
 8. Ahousing and cover assembly for use with electrical components including:a housing member; means for mounting electrical components in saidhousing member; line access means for providing line ingress and egressfrom said housing member, said housing member having equipment accessopening means having substantially circular sidewalls tapering outwardlywith respect to said housing member and tapering inwardly with respectto said opening, said sidewalls having threads extending away from saidsidewalls on the external face thereof, said sidewall having theconfiguration of a truncated cone, said cone having an included angle ofabout 30*; a cover over said opening, said cover having a substantiallycircular mouth having an inner wall having the configuration of atruncated cone, the wall of the mouth having threads on the inner facethereof, said mouth and said threads being mated with the threads onsaid sidewalls of said housing; said cover including releasable lockmeans extending axially between opposing portions of said cover andhousing member, said lock means comprising a slideable bolt, bias meansfor urging the extension of said bolt axially, release means formanually retracting the bolt; socket means on said housing engaging saidbolt, said socket means being positioned to engage said bolt to lock thecover against rotation with respect to said housing at a point withinabout 10* rotation ahead of that point of rotation at which zeroclearance would be obtained between the threads on the housing memberand the cover; said bolt having a reach less than the axial distancebetween adjacent threads on said sidewalls.